Method For Reducing The Nitrogen Content Of Petroleum Streams With Reduced Sulfuric Acid Consumption

ABSTRACT

The instant invention relates to a multi-stage process for producing low-nitrogen hydrocarbonaceous boiling range products involving contacting a hydrocarbonaceous feedstream with an acidic solution to selectively remove heterocyclic nitrogen-containing compounds, recovering the used sulfuric acid solution, and cascading the used sulfuric acid solution to another downstream contacting stage.

FIELD OF THE INVENTION

The instant invention relates to a method for upgradingnitrogen-containing hydrocarbon streams. More particularly, the presentinvention relates to a method for producing low-nitrogen hydrocarbonproducts involving contacting a hydrocarbon feedstream with an acidicsolution to selectively remove heterocyclic nitrogen-containingcompounds, recovering a used sulfuric acid solution, and cascading theused sulfuric acid solution to another contacting stage.

BACKGROUND OF THE INVENTION

Currently, there exists a need to reduce the sulfur and aromaticscontent of motor fuels, in particular diesel, to meet currentenvironmental emission regulations. While both the sulfur and aromaticscontent of diesel boiling range feedstreams from which diesel motorfuels are derived can be reduced to a satisfactory level through the useof catalytic treatments, the catalytic treatments are severely impededby nitrogen-containing compounds present in the feedstream. Thus, manymethods for reducing the nitrogen content in feedstreams, such as thoseused in sulfur and aromatics reducing processes, for motor fuelproduction have been proposed.

For example, U.S. Pat. No. 3,719,587 teaches the use of dilute sulfuricacid (0-10 wt %) to remove basic nitrogen species from coal liquifactionderived naphtha. Unfortunately, hydrotreating catalysts are not onlypoisoned by basic nitrogen species, but also by non-basic nitrogenheterocycles that are abundant in diesel boiling range feedstreams. Forthis reason, stronger sulfuric acid has been used to removesubstantially all of the nitrogen species.

There also exists a need to reduce the heterocyclic nitrogen content offeedstreams used in the lube oil processes because heterocyclicnitrogen-containing compounds, especially basic heterocyclicnitrogen-containing compounds, contained in lube oil boiling rangefeedstreams act as competitive inhibitors on the catalytic sites ofcatalysts. These nitrogen-containing compounds are indigenous to crudeoils, and are typically concentrated in the higher boiling fractions,such as lube oil fractions. The presence of these heterocyclicnitrogen-containing compounds typically prevents lube oil hydroprocessesfrom operating as effectively and/or efficiently as possible. Forexample, the presence of these heterocyclic nitrogen-containingcompounds in lube oil boiling range feedstreams used in hydrocrackingoperations requires that the hydrocracking be performed at hightemperatures that impart a higher degree of over-cracking and lube oilboiling range yield loss when compared to hydrocracking processes thatoperate at a lower temperature.

Also, the removal of nitrogen species from lube oil boiling rangefeedstreams allow cracking operations to operate more efficientlybecause these heterocyclic nitrogen-containing compounds, especiallybasic heterocyclic nitrogen-containing compounds, act as competitiveinhibitors on the acidic cracking sites of cracking catalysts. Thus,many methods for reducing the nitrogen content in feedstreams have beenproposed.

Also, United States Statutory Invention Registration H1368, Fraytet,teaches the use of concentrated sulfuric acid, i.e. at least 95 wt. %sulfuric acid, to treat straight run jet fuel boiling range streams. Theprocess requires that the sulfuric acid-containing stream be dispersedin the jet fuel in the form of droplets smaller than about 300 microns.The Fraytet process discloses that 90% or more of the nitrogen can beremoved from the jet fuel boiling range stream. However, as Fraytetpoints out, separation of the acid from the feedstream is critical toavoid unwanted secondary reactions from occurring, such as, for example,polymerization of olefins and reaction of sulfuric acid with thiophenicspecies. These unwanted reactions are detrimental in several ways. Firstthe unwanted side reactions force the practitioner of these processes toutilize more sulfuric acid because these reactions consume a portion ofthe sulfuric acid. Secondly, it degrades the product by forminghigh-boiling polymers from olefinic materials, which become soot-formersin subsequent combustion. Finally, some of the byproducts from theseunwanted reactions are removed due to solubility in the acid byproductand lead to an overall yield loss for the process.

However, it is also known in the art that dispersive contacting methodssuch as those of Fraytet have certain drawbacks such as “pepper sludge”formation. Pepper sludge formation occurs when the tiny droplets of acidare not readily coalesced or settled in gravity settlers. The dispersedacidic material suspended in the feed is thus carried over with thetreated feed, and practitioners of such processes are forced to utilizecaustic treatments to neutralize the pepper sludge and avoid corrosionproblems. However, the “pepper sludge” suspended in the feed alsocontains nitrogen species that were removed from the feed. Uponneutralization, the nitrogen species may be liberated and return to thefeed. Thus, the existence of pepper sludge in dispersive treatmentmethods limits the ultimate level of nitrogen reduction that can beachieved. Therefore, there exists a need in the art for a more effectivenitrogen removal method for diesel boiling range feedstreams.

Therefore, there still exists a need in the art for a more effectivenitrogen removal method for hydrocarbon feedstreams which benefits thesubsequent hydroprocessing of the hydrocarbon feedstreams, i.e. aprocess that more selectively removes nitrogen-containing heterocyclesthat poison hydroprocessing catalysts without incurring the debitslisted above that are the result of unwanted chemistry.

SUMMARY OF THE INVENTION

The instant invention is directed at an improved hydroprocessing processfor hydrocarbon feedstreams containing nitrogen contaminants. Theprocess comprises:

-   -   a) providing a sulfuric acid solution having a sulfuric acid        concentration of at least about 75 wt. %, based on the sulfuric        acid solution;    -   b) contacting a first hydrocarbon feedstream containing nitrogen        heteroatoms and having a Total Acid Number in a first contacting        stage with the sulfuric acid solution under conditions effective        at removing at least about 80 wt. % of the nitrogen heteroatoms        contained in said hydrocarbon feedstream thereby producing at        least a first stage effluent comprising at least a first        hydrocarbon product stream and a first used sulfuric acid        solution, wherein the volumetric treat rate of the sulfuric acid        solution is greater than about 0.5 vol. %, based on the first        hydrocarbon feedstream;    -   c) separating said first used sulfuric acid solution and said        first hydrocarbon product stream;    -   d) cascading at least a portion of said first used sulfuric acid        solution to a second contacting stage;    -   e) contacting a second hydrocarbon feedstream containing        nitrogen heteroatoms and having a Total Acid Number in the        second contacting stage with the first used sulfuric acid        solution under conditions effective at removing at least about        80 wt. % of the nitrogen heteroatoms contained in said second        hydrocarbon feedstream thereby producing at least a second stage        effluent comprising at least a second hydrocarbon product stream        and a second used sulfuric acid solution, wherein the volumetric        treat rate of the first used sulfuric acid solution is greater        than about 0.5 vol. %, based on the second hydrocarbon        feedstream, wherein the concentration of nitrogen heteroatoms in        said second hydrocarbon feedstream is higher than that of said        first hydrocarbon feedstream;    -   f) separating said second used sulfuric acid solution and said        second hydrocarbon product stream; and    -   g) contacting at least a portion of said first product stream        with a hydroprocessing catalyst in a hydroprocessing reaction        stage.

In one embodiment of the instant invention the sulfuric acid solution isa spent sulfuric acid solution obtained from an alkylation process unitwherein the spent sulfuric acid solution is produced by:

-   -   a) combining an olefinic hydrocarbon feedstream containing C₄        olefins with isobutane to form a hydrocarbonaceous mixture; and    -   b) contacting the hydrocarbonaceous mixture with sulfuric acid        under conditions effective for producing at least an alkylate        and a sulfuric acid solution having an acid concentration of at        least about 75 wt. %.

In another embodiment of the instant invention, at least a portion ofthe second hydrocarbon product stream is also contacted with ahydroprocessing catalyst in a hydroprocessing reaction stage.

In another embodiment of the instant invention the process furthercomprises separately contacting the first and second hydrocarbon productstreams with an effective amount of an acid reducing material selectedfrom caustic and water under conditions effective at reducing the totalacid number of the hydrocarbon products prior to hydroprocessing.

In another preferred embodiment of the instant invention, the contactingof the first and second hydrocarbon product streams with the acidreducing material reduces the total acid number of the first and secondhydrocarbon product streams to at least the total acid number of thefirst and second hydrocarbon feedstreams, respectively.

DETAILED DESCRIPTION OF THE INSTANT INVENTION

The instant invention is an improved hydroprocessing process involvingremoving nitrogen from hydrocarbon feedstreams containing both nitrogenand sulfur contaminants. The present invention involves contacting ahydrocarbon feedstream having a total acid number and containing bothnitrogen and sulfur contaminants with a sulfuric acid solution therebyproducing at least a first effluent comprising at least a firsthydrocarbon product stream and a first used sulfuric acid solution,wherein the volumetric treat rate of the sulfuric acid solution isgreater than about 0.5 vol. %, based on the first hydrocarbonfeedstream. The first stage effluent is then separated into a first usedsulfuric acid solution and a first hydrocarbon product stream. At leasta portion of the first used sulfuric acid solution is cascaded to asecond contacting stage. In the second contacting stage a secondhydrocarbon feedstream containing nitrogen heteroatoms and having aTotal Acid Number is contacted with the first used sulfuric acidsolution under conditions effective at removing at least about 80 wt. %of the nitrogen heteroatoms contained in the second hydrocarbonfeedstream. It should be noted that the concentration of nitrogenheteroatoms in the second hydrocarbon feedstream is higher than that ofthe first hydrocarbon feedstream. The second contacting stage produces asecond effluent comprising at least a second hydrocarbon product streamand a second used sulfuric acid solution. The second stage effluent isthe separated into a second used sulfuric acid solution and a secondhydrocarbon product stream. At least a portion of the first productstream is then contacted with a hydroprocessing catalyst in ahydroprocessing reaction stage.

It should be noted that “hydrocarbon feedstream” as used herein is meantto refer to a hydrocarbon feedstream containing both nitrogen and sulfurcontaminants and possessing a Total Acid Number (“TAN”).

The first and second hydrocarbon feedstreams suitable for treatment inthe present invention boil above 300° F. and include those streamsconsidered to boil within the distillate range through the lube oilrange. As used herein, distillate boiling range includes streams boilingin the range of about 300° F. to about 775° F., preferably about 350° F.to about 750° F., more preferably about 400° F. to about 700° F, mostpreferably about 450° F. to about 650° F. These include distillateboiling range feedstreams that are not hydrotreated, are a blend ofnon-hydrotreated distillate boiling range feedstreams, previouslyhydrotreated distillate boiling range feedstreams, blends ofhydrotreated distillate boiling range feedstreams, and blends ofnon-hydrotreated and hydrotreated distillate boiling range feedstreams.The distillate boiling range feedstreams suitable for use herein canalso contain greater than 10%, based on the distillate boiling rangefeedstream, of cracked stock. It should be noted that a hydrotreateddistillate boiling range feedstream is to be considered a feedstreamthat has been contacted with an effective hydrotreating catalyst undereffective hydrotreating conditions prior to being contacted with asulfuric acid solution.

Distillate boiling range feedstreams as used herein typically have anitrogen content as high as about 2500 wppm nitrogen, preferably about50 to about 2500 wppm nitrogen, more preferably about 75 to about 1000wppm nitrogen, and most preferably about 100 to about 750 wppm nitrogen.The nitrogen appears as both basic and non-basic nitrogen species.Non-limiting examples of basic nitrogen species may include quinolinesand substituted quinolines, and non-limiting examples of non-basicnitrogen species may include carbazoles and substituted carbazoles. Thesulfur content of such streams is typically about 40 wppm to about 35000wppm sulfur, preferably about 250 wppm to about 35000 wt. % sulfur.

Lube oil boiling range feedstreams as used herein includes anyconventional lube oil boiling range feedstreams used in lube oilprocessing. Such feedstreams typically include wax-containingfeedstreams such as feeds derived from crude oils, shale oils and tarsands as well as synthetic feeds such as those derived from theFischer-Tropsch process. Typical wax-containing feedstocks for thepreparation of lubricating base oils have initial boiling points ofabout 599° F. (315° C.) or higher. Non-limiting examples of lube oilboiling range feedstreams include feeds such as reduced crudes,hydrocrackates, extracts, hydrotreated oils, atmospheric gas oils,vacuum gas oils, coker gas oils, atmospheric and vacuum resids,deasphalted oils, slack waxes, raffinates, and Fischer-Tropsch wax. Suchfeeds may be derived from distillation towers (atmospheric and vacuum),hydrocrackers, hydrotreaters and solvent extraction units, and may havewax contents of up to 50% or more. Preferred lube oil boiling rangefeedstreams boil above about 650° F. (343° C.).

As mentioned above, raffinates are suitable for use in the presentprocess. Lube oil boiling range raffinates are produced by solventextracting a lube oil boiling range feedstream, such as those describedabove. In this embodiment, the lube oil raffinates so produced boilwithin the range described above and preferred lube oil boiling rangeraffinates boil above about 650° F. (343° C.). The lube oil boilingraffinate may also comprise mixtures of lube oil raffinates boilingwithin the above-defined parameters. Thus, more than one lube oilboiling range feedstream can be solvent extracted, and the resultinglube oil boiling range raffinates combined to form one lube oil boilingrange raffinate that is contacted with the sulfuric acid solution. Thelube oil raffinates may be either fully or partially extracted, i.e.under-extracted. By under-extracted it is meant that, the extraction iscarried out under conditions such that the raffinate yield is maximizedwhile still removing most of the lowest quality molecules from the feed.Raffinate yield may be maximized by controlling extraction conditions,for example, by lowering the solvent to oil treat ratio and/ordecreasing the extraction temperature.

Lube oil raffinates used herein can be produced under standard solventextracting conditions, and the conditions chosen are not critical aslong as the raffinate so produced meets the above-described boilingrange criteria. Typically, the solvent extracting process involvescontacting a lube oil boiling range stream with an extraction solvent.The extraction solvent can be any solvent known that has an affinity foraromatic hydrocarbons in preference to non-aromatic hydrocarbons.Non-limiting examples of such solvents include sulfolane, furfural,phenol, and N-methyl pyrrolidone (“NMP”). Furfural, phenol, and NMP arepreferred.

The lube boiling range stream can be contacted with the extractionsolvent by any suitable solvent extraction method. Non-limiting examplesof such include batch, semi-batch, or continuous. It is preferred thatthe extraction process be a continuous process, and it is more preferredthat the continuous process be operated in a counter-current fashion. Ina counter-current configuration, it is preferred that the lube oilboiling range feedstream be introduced into the bottom of an elongatedcontacting zone or tower and caused to flow in an upward direction whilethe first extraction solvent is introduced at the top of the tower andallowed to flow in a downward direction, counter-current to theupflowing lube oil boiling range feedstream. In this configuration, thelube oil boiling range feedstream is forced to pass counter-currently tothe extraction solvent resulting in the intimate contact between theextraction solvent and the lube oil boiling range feedstream. Theextraction solvent and the light lube stream migrate to opposite ends ofthe contacting zone.

The conditions under which the extraction solvent is contacted with thelube oil boiling range feedstream can be any conditions known to beeffective in the solvent extraction of lube oil boiling rangefeedstreams. In a preferred embodiment, the temperature and pressure areselected to prevent complete miscibility of lube oil boiling rangefeedstream in the extraction solvent.

The contacting of the lube oil boiling range feedstream with theextraction solvent produces at least a first aromatics-rich extractsolution and a first aromatics-lean raffinate solution. It should benoted that as used herein, aromatics-lean is meant to refer to theconcentration of aromatics present in the raffinate phase produced bysolvent extraction in relation to the concentration of aromatics presentin the extract phase produced by solvent extraction. The firstaromatics-lean raffinate solution is then treated to remove at least aportion of the extraction solvent contained therein, thus producing thelube oil boiling range raffinate that can be used herein. The removal ofat least a portion of the extraction solvent can be done by any meansknown in the art effective at separating at least a portion of anextraction solvent from an aromatics lean raffinate solution. Preferablythe lube oil boiling range raffinate is produced by separating at leasta portion of the first extraction solvent from the first aromatics-richextract solution in a stripping or distillation tower. By at least aportion, it is meant that at least about 80 vol %, preferably about 90vol %, more preferably 95 vol %, based on the first aromatics-leanraffinate solution, of the extraction solvent is removed from thearomatics-lean raffinate solution. Most preferably substantially all ofthe extraction solvent is removed from the aromatics-lean raffinatesolution. It should be noted that when the solvent extracting methodthat produces the lube oil boiling range raffinate is referenced herein,it is meant to encompass this separation step.

Lube oil boiling range feedstreams typically contain greater than about100 wppm nitrogen, more typically the nitrogen concentration ranges fromabout 1000 wppm to about 2000 wppm. The nitrogen compounds appear asboth basic and non-basic nitrogen species in the lube oil boiling rangefeedstreams. Again, non-limiting examples of basic nitrogen species mayinclude quinolines and substituted quinolines, and non-limiting examplesof non-basic nitrogen species may include carbazoles and substitutedcarbazoles.

In practicing the instant invention, a first hydrocarbon feedstream isintimately contacted with a sulfuric acid solution. The sulfuric acidsolution used herein is suited for the composition of the hydrocarbonfeedstream treated. However, typical acid solutions contain greater thanabout 75 wt. % sulfuric acid, based on the sulfuric acid solution,preferably greater than about 80 wt. %, and more preferably about 85 toabout 93 wt. %. The sulfuric acid solution may be obtained through anymeans known. It is preferred that the sulfuric acid solution be thespent acid from an alkylation process unit having a sulfuric acidconcentration within the above-defined ranges. A typical alkylationprocess involves combining an olefinic hydrocarbon feedstream containingC₄ olefins with isobutane to produce a hydrocarbonaceous mixture. Thishydrocarbonaceous mixture is subsequently contacted with sulfuric acid.The sulfuric acid used for contacting the hydrocarbonaceous mixture istypically reagent grade sulfuric acid having an acid concentration of atleast about 95 wt. %. Preferably the sulfuric acid has a sulfuric acidconcentration of greater than about 97 wt. %. The hydrocarbonaceousmixture is contacted with the sulfuric acid under conditions effectiveat producing at least an alkylate and a spent sulfuric acid solution.The latter is sometimes referred to as “spent alkylation acid”. Thesulfuric acid solution so produced comprises at least about 75 wt. %sulfuric acid, based on the sulfuric acid solution, preferably greaterthan about 80 wt %, more preferably about 85 wt. % to about 92 wt %,about 0.5 to about 5 wt. % water, with the remaining balance being acidsoluble hydrocarbons. It is more preferred that the effective conditionsbe selected such that the sulfuric acid solution so produced comprisesbetween about 82 and 95 wt. % sulfuric acid, about 3 to about 10 wt %water, with the remaining balance being soluble hydrocarbons. However,it is most preferred that the effective conditions be selected such thatthe sulfuric acid solution so produced comprises between about 85 and 93wt. % sulfuric acid, about 4 to about 8 wt. % water, with the remainingbalance being soluble hydrocarbons.

As mentioned above, the concentration of sulfuric acid in the sulfuricacid solution is dependent on the type of stream treated. If the firsthydrocarbon feedstream is a non-hydrotreated distillate or a blend ofnon-hydrotreated distillates, the sulfuric acid solution preferably hasan acid concentration of greater than about 76 wt. %, a waterconcentration of about 2 wt. % to about 12 wt. %, and a dissolved oilconcentration of less than about 12 wt. %; more preferably an acidconcentration of about 85 wt. % to about 89 wt. %, a water concentrationof about 6 wt. % to about 10 wt. %, and a dissolved oil concentration ofabout 5 wt. % to about 9 wt. %. If the distillate stream is ahydrotreated distillate, or a blend of hydrotreated distillates, each ofwhich may or may not contain cracked stock, the sulfuric acid solutionpreferably has an acid concentration of greater than about 79 wt. %, awater concentration of about 2 wt. % to about 9 wt. %, and a dissolvedoil concentration of less than about 12 wt. %; more preferably an acidconcentration of about 88 wt. % to about 93 wt. %, a water concentrationof about 4 wt. % to about 6 wt. %, and a dissolved oil concentration ofabout 5 wt. % to about 10 wt. %. If the distillate stream is anon-hydrotreated distillate or a blend of distillates, containinggreater than 10% cracked stock, based on the distillate or blend, thesulfuric acid solution preferably has an acid concentration of greaterthan about 79 wt. %, a water concentration of about 2 wt. % to about 9wt. %, and a dissolved oil concentration of less than about 12 wt. %;more preferably an acid concentration of about 84 wt. % to about 91 wt.%, a water concentration of about 5 wt. % to about 10 wt. %, and adissolved oil concentration of about 5 wt. % to about 12 wt. %.

If the first hydrocarbon feedstream is a lube oil boiling rangefeedstream, excluding raffinates, the sulfuric acid solution used hereincontains at least about 75 wt. % sulfuric acid, based on the sulfuricacid solution, preferably greater than about 80 wt. %, more preferablyabout 85 wt. % to about 93 wt. %. Therefore, the spent alkylation acidproduced from the alkylation process unit contains about 0.5 to about 5wt. % water, with the remaining balance being acid suspendedhydrocarbons. If the hydrocarbon feedstream is a lube oil boiling rangefeedstream, it is more preferred that the alkylation unit be run undereffective conditions selected such that the sulfuric acid solution soproduced comprises between about 82 and 92 wt. % sulfuric acid, about 1to about 4 wt. % water, with the remaining balance being suspendedhydrocarbons; however, it is most preferred that the effectiveconditions be selected such that the sulfuric acid solution so producedcomprises between about 85 and 93 wt. % sulfuric acid, about 1.5 toabout 4 wt. % water, with the remaining balance being suspendedhydrocarbons.

If the first hydrocarbon feedstream is a raffinate, the sulfuric acidsolution used contains at least about 75 wt. % sulfuric acid, based onthe sulfuric acid solution, preferably greater than about 85 wt. %, morepreferably about 92 wt. % to about 98 wt. %. If the sulfuric solution isspent sulfuric acid, the alkylation process unit is run under conditionseffective at producing a sulfuric acid solution comprising at leastabout 75 wt. % sulfuric acid, based on the sulfuric acid solution,preferably greater than about 80 wt. % sulfuric acid, more preferablyabout 80 vol. % to about 95 wt. % sulfuric acid. Again, the sulfuricacid solution also typically contains about 0.5 to about 5 wt. % water,with the remaining balance being acid suspended hydrocarbons. It is morepreferred that the effective conditions be selected such that thesulfuric acid solution so produced comprises between about 82 and 92 wt.% sulfuric acid, about 1 to about 4 wt. % water, with the remainingbalance being suspended hydrocarbons. However, it is most preferred thatwhen the first hydrocarbon feedstream is a raffinate that the effectiveconditions of the alkylation process unit be selected such that thesulfuric acid solution so produced comprises between about 92 and 98 wt.% sulfuric acid, about 1.5 to about 4 wt. % water, with the remainingbalance being suspended hydrocarbons.

It should be noted that it is within the scope of the present inventionto dilute the sulfuric acid solution obtained from the alkylation unit,or otherwise, with a suitable diluent, preferably water, in order toprovide a sulfuric acid solution having the above-describedconcentration of sulfuric acid, i.e. greater than about 75 wt. %sulfuric acid, etc. In order to determine the sulfuric acidconcentration once the diluent has been added to the sulfuric acidsolution, the sulfuric acid content and water content are measured bystandard analytical techniques. The equivalent acid strength can then becalculated with the following formula: equivalent wt % sulfuric acid=wt% sulfuric acid/(wt % sulfuric acid+wt % water). In this formula, theacid soluble hydrocarbon content of the spent alkylation acid is treatedas an inert diluent with respect to the sulfuric acid and water content.

The first hydrocarbon feedstream is contacted with the sulfuric acidsolution in a first contacting stage. The treat rate of the sulfuricacid solution in the contacting stages used herein is also dependent onthe type of hydrocarbon feedstream used. Distillate boiling range andlube oil boiling range feedstreams are contacted with the sulfuric acidsolution at an acid volumetric treat rate of greater than about 0.5 vol.%, based on the distillate boiling range feedstream, preferably about 1to about 10 vol. %, and more preferably 1 to about 6 vol. %. If thedistillate boiling range feedstream contains greater than about 40 wt. %cracked stock, then the most preferred treat rates are about 2 vol. % toabout 6 vol. %, based on the distillate boiling range feedstream.Raffinates are contacted with the sulfuric acid solution at an acidvolumetric treat rate of greater than about 0.1 vol. %, based on thelube oil boiling range raffinate, preferably greater than about 0.5 vol.% more preferably about 0.5 vol. % to about 2.0 vol. %.

The contacting of the hydrocarbon feedstream and the sulfuric acidsolution in the first contacting stage can be achieved by any suitablemethod including both dispersive and non-dispersive methods.Non-limiting examples of suitable dispersive methods include mixingvalves, mixing tanks or vessels, and other similar devices. Non-limitingexamples of non-dispersive methods include packed beds of inertparticles and fiber film contactors such as those sold by MerichemCompany and described in U.S. Pat. No. 3,758,404, which is herebyincorporated by reference, which involve contacting along a bundle ofmetallic fibers rather than a packed bed of inert particles. Preferredcontacting methods are non-dispersive, and more preferred contactingmethods are those that are classified as dispersive.

The contacting of the hydrocarbon feedstream with the sulfuric acidsolution in the first contacting stage occurs under effectiveconditions. Effective conditions are also dependent on the type ofhydrocarbon feedstream used. If the hydrocarbon feedstream is adistillate boiling range feedstream or a raffinate, effective conditionsare to be considered those conditions that allow for a reduction of thenitrogen content of the distillate boiling range feedstream by greaterthan about 80 wt. %, preferably greater than about 85 wt. % morepreferably greater than about 90 wt. %. Effective conditions are also tobe considered those conditions that minimize yield losses during thesulfuric acid solution treatment to about 0.5 to about 6 wt. %,preferably about 0.5 to about 4 wt. %, and more preferably about 0.5 toabout 3 wt. %. If the hydrocarbon feedstream is a lube oil boiling rangefeedstream, excluding raffinates, effective conditions are to beconsidered those conditions that allow the present method to achieve areduction of nitrogen of at least about 60 wt. %, preferably greaterthan about 75 wt. %, more preferably greater than 80 wt. %.

The contacting of the first hydrocarbon feedstream with the sulfuricacid solution in the first contacting stage produces a first stageeffluent comprising at least a first hydrocarbon product stream and afirst used sulfuric acid solution. The first used sulfuric acidsolution, which now contains the removed nitrogen species, is thenseparated from the first hydrocarbon product stream. The first usedsulfuric acid solution and the first hydrocarbon product stream can beseparated by any means known to be effective at separating an acid froma hydrocarbon stream. Non-limiting examples of suitable separationmethods include gravity settling, electric field induced settling,centrifugation, microwave induced settling and settling enhanced withcoalescing surfaces. However, it is preferred that the first hydrocarbonproduct stream and the first used sulfuric acid solution be separated,or allowed to separate, into layers in a separation device such as asettling tank or drum, coalescer, electrostatic precipitator, or othersimilar device. In one embodiment, the above-described fiber-filmcontactors can be used for separating the first used sulfuric acidsolution and the first hydrocarbon product stream. The first hydrocarbonproduct stream is withdrawn from the separation device and conducted toa suitable hydroprocessing process.

After the first used sulfuric acid solution and the first hydrocarbonproduct have been separated, the first used sulfuric acid solution iscascaded to a second contacting stage. It is preferred that the firstused sulfuric acid solution have an acid concentration within the rangesdiscussed above. For example, if the second hydrocarbon feedstream is adistillate boiling range feedstream, it is preferred that the first usedsulfuric acid solution have an acid concentration within the rangesdiscussed above for distillate boiling range feedstreams.

In the second contacting stage, a second hydrocarbon feedstream iscontacted with the first used sulfuric acid solution. The secondhydrocarbon feedstream can be any of those described above. However, thesecond hydrocarbon feedstream is a higher nitrogen content feedstreamthan the first hydrocarbon feedstream. Preferably the nitrogen level ofthe second hydrocarbon feedstream is about 100% to about 1000% higherthan that of the first hydrocarbon feedstream.

The second hydrocarbon feedstream is contacted with the first usedsulfuric acid solution under effective conditions. Effective conditionsare to be considered any of those discussed above in reference to thefirst contacting stage, and are also dependent on the make-up of thesecond hydrocarbon feedstream. For example, if the second hydrocarbonfeedstream is a distillate boiling range feedstream, effectiveconditions are to be considered those effective conditions discussedabove in relation to distillate boiling range feedstreams.

The contacting of the second hydrocarbon feedstream with the sulfuricacid solution in the second contacting stage produces a second stageeffluent comprising at least a second hydrocarbon product stream and asecond used sulfuric acid solution. The second used sulfuric acidsolution, which now contains the removed nitrogen species, is thenseparated from the second hydrocarbon product stream. The second usedsulfuric acid solution and the second hydrocarbon product stream can beseparated by any means discussed above in relation to the firsthydrocarbon product stream and first sulfuric acid solution.

As discussed above, the first hydrocarbon product stream is conducted toa suitable hydroprocessing process. Hydroprocessing, as used herein, ismeant to refer to any catalytic process using hydrogen treat gas in thepresence of a hydroprocessing catalyst designed to facilitate thedesired reaction. Non-limiting examples of suitable hydroprocessingprocesses include hydrotreating, hydrocracking, ring opening, aromaticssaturation, hydrodewaxing, and hydrofinishing. It should be noted thatthe hydroprocessing process should be selected according to the desiredreaction and the make-up of the first hydrocarbon product stream. Itshould also be noted that if the first hydrocarbon product streamresults from a lube oil boiling range feedstream, this product streamcan also be conducted to a solvent dewaxing process.

In one embodiment of the instant invention, the second hydrocarbonproduct stream is also conducted to a suitable hydroprocessing process.Suitable hydroprocessing processes are those discusses above, and if thesecond hydrocarbon product stream results from a lube oil boiling rangefeedstream, this product stream can also be conducted to a solventdewaxing process.

The sulfuric acid treatment of the first and second hydrocarbonfeedstreams discussed above, however, also results in hydrocarbonproduct streams that are typically more acidic than the hydrocarbonfeedstream used in the production of the hydrocarbon product stream. Forexample, the first hydrocarbon product stream is typically more acidicthan the first hydrocarbon product stream. The measure of acidityreferenced herein is the total acid number (“TAN”) of the feedstream orproduct stream. The TAN is the quantity of base, expressed as milligramsof potassium hydroxide per gram of sample, required to titrate a sampleto a specified end point, as measured by ASTM method D-664. A moreacidic hydrocarbon product stream can have a detrimental effect onprocessing equipment, etc. because of its corrosive nature. Thus, oneembodiment of the instant invention involves separately contacting thefirst and second hydrocarbon product streams, prior to hydroprocessing,with an effective amount of an acid-reducing material selected fromcaustic and water, preferably water. By an effective amount of material,it is meant that amount of material that reduces the TAN of thehydrocarbon product stream. The hydrocarbon product streams arecontacted with the acid reducing material under effective conditions. Byeffective conditions, it is meant those conditions, that when selected,allow for the reduction of the TAN of the hydrocarbon product stream.Preferably the effective amount of acid reducing material and theeffective conditions are selected such that the TAN of the hydrocarbonproduct streams are equal that of their respective hydrocarbonfeedstreams. More preferably the effective amount of the acid reducingmaterial and the effective conditions are selected such that the TAN ofthe hydrocarbon product streams is lower than that of their respectivehydrocarbon feedstreams

In one embodiment, the hydrocarbon product streams will also typicallyhave a sulfur concentration lower than that of their correspondinghydrocarbon feedstreams. Thus, the contacting of the hydrocarbonfeedstreams in the first and second contacting stages with the sulfuricacid solutions also reduces the sulfur content of the respectivehydrocarbon product streams. However, it is desirable to minimize thereduction of sulfur to minimize yield losses. Typically the first andsecond hydrocarbon product stream will have a sulfur content about 0.1to about 25% lower than their respective hydrocarbon feedstreams,preferably about 0.1 to about 5% lower.

The above description is directed to several embodiments of the presentinvention. Although the above description is directed at the use of onlytwo contacting stages, the inventors hereof contemplate the use of morethan two contacting stages. For example, the second stage sulfuric acidsolution can be cascaded to a third contacting stage and contacted witha third hydrocarbon stream having a nitrogen concentration lower thanthat of the second hydrocarbon feedstream, etc. The limiting factor onthe number of contacting stages shall typically be the strength of thesulfuric acid solution because it must still have sufficient strength toperform the desired reduction of nitrogen. Thus, those skilled in theart will recognize that other embodiments that are equally effectivecould be devised for carrying out the spirit of this invention.

The following examples will illustrate the improved effectiveness of thepresent invention, but is not meant to limit the present invention inany fashion.

EXAMPLES Example 1

A 100N lube raffinate having 18 wppm nitrogen and 6350 wppm sulfur wastreated with a spent alkylation unit acid solution at a volumetric treatrate of 0.5 vol. %, based on the raffinate. The sulfuric acid had anequivalent sulfuric acid concentration of 96 wt. %

40 ml of the raffinate was placed in a 100 cc centrifuge tube and warmedin a water bath to 60° C. to melt its wax content. 0.2 ml of the spentalkylation acid solution was then added and the centrifuge tube wasshaken by hand for 60 seconds and the mixture was then centrifuged at1500 rpm for 10 minutes. The raffinate hydrocarbon product was thenpoured away from the used sulfuric acid solution and analyzed. Thenitrogen content was reduced to 1 wppm.

The used sulfuric acid solution was left in the centrifuge tube and 8.7grams 10 mls of a diesel boiling range hydrocarbon having 388 wppmnitrogen and 1.79 wt. % sulfur was added to the centrifuge tubecontaining the used sulfuric acid solution. The centrifuge tube wasagain shaken by hand for 60 seconds and centrifuged at 1500 rpm for 10minutes. The diesel hydrocarbon product was then poured away from theused sulfuric acid solution, weighed and analyzed. The dieselhydrocarbon product weighed 8.6 grams, which represents recovering 99%of the weight of the diesel added to the sulfuric acid solution. Theacid byproduct product in this case was a fluid at room temperature.

The treated diesel was washed with water and analyzed by ANTEK fornitrogen and sulfur. The diesel product contained 95 wppm N and 1.58 wt.% sulfur.

Example 2 (Comparative Example)

40 ml of the same diesel hydrocarbon as in example 1 was placed in a 100cc centrifuge tube and 0.8 ml of the spent alkylation acid solution wasthen added. The centrifuge tube was shaken by hand for 60 seconds andcentrifuged at 1500 rpm for 10 minutes. The diesel hydrocarbon productwas then poured away from the used sulfuric acid solution, weighed andanalyzed. The acid byproduct was a tarry, viscous fluid at roomtemperature. The treated diesel was washed with water and analyzed byANTEK for nitrogen and sulfur. The diesel product contained 158 wppm Nand 1.58 wt. % sulfur. A total of 96 wt % of diesel product wasrecovered, representing a 4 wt % yield loss to the acid.

While not wishing to be limited by theory, the inventors hereof believethat by pre-equilibrating the acid with heavy molecules by treating the100N raffinate, the used sulfuric acid solution has a reduced capacityto remove similar molecules from the diesel by simple equilibration.

1. An improved hydroprocessing process for hydrocarbon feedstreamscontaining nitrogen and sulfur contaminants comprising: a) providing asulfuric acid solution having a sulfuric acid concentration of at leastabout 75 wt. %, based on the sulfuric acid solution; b) contacting afirst hydrocarbon feedstream containing nitrogen and sulfur heteroatomsand having a Total Acid Number in a first contacting stage with thesulfuric acid solution under conditions effective at removing at leastabout 60 wt. % of the nitrogen heteroatoms contained in said hydrocarbonfeedstream thereby producing at least a first stage effluent comprisingat least a first hydrocarbon product stream and a first used sulfuricacid solution, wherein the volumetric treat rate of the sulfuric acidsolution is greater than about 0.5 vol. %, based on the firsthydrocarbon feedstream; c) separating said first used sulfuric acidsolution and said first hydrocarbon product stream; d) cascading atleast a portion of said first used sulfuric acid solution to a secondcontacting stage; e) contacting a second hydrocarbon feedstreamcontaining nitrogen heteroatoms and having a Total Acid Number in thesecond contacting stage with the first used sulfuric acid solution underconditions effective at removing at least about 60 wt. % of the nitrogenheteroatoms contained in said second hydrocarbon feedstream therebyproducing at least a second stage effluent comprising at least a secondhydrocarbon product stream and a second used sulfuric acid solution,wherein the volumetric treat rate of the first used sulfuric acidsolution is greater than about 0.5 vol. %, based on the secondhydrocarbon feedstream, wherein the concentration of nitrogenheteroatoms in said second hydrocarbon feedstream is higher than that ofsaid first hydrocarbon feedstream; f) separating said second usedsulfuric acid solution and said second hydrocarbon product stream; andg) contacting at least a portion of said first and/or second hydrocarbonproduct stream with a hydroprocessing catalyst in a hydroprocessingreaction stage.
 2. The process according to claim 1 wherein said firstand second hydrocarbon feedstreams are selected from those hydrocarbonfeedstreams boiling above about 300° F.
 3. The process according toclaim 1 wherein said first and second hydrocarbon feedstreams areselected from distillate boiling range feedstreams and lube oil boilingrange feedstreams.
 4. The process according to claim 3 wherein saiddistillate boiling range feedstreams are selected from distillateboiling range feedstreams that are not hydrotreated, are a blend ofnon-hydrotreated distillate boiling range feedstreams, previouslyhydrotreated distillate boiling range feedstreams, blends ofhydrotreated distillate boiling range feedstreams, blends ofnon-hydrotreated and hydrotreated distillate boiling range feedstreams,and said lube oil boiling range feedstreams are selected from reducedcrudes, hydrocrackates, extracts, hydrotreated oils, atmospheric gasoils, vacuum gas oils, coker gas oils, atmospheric and vacuum resids,deasphalted oils, slack waxes, raffinates, and Fischer-Tropsch wax, andmixtures thereof.
 5. The process according to claim 1 wherein the firstand second hydrocarbon feedstreams contain about 25-2500 wppm nitrogen.6. The process according to claim 5 wherein the 25-2500 wppm nitrogenincludes carbazole and/or substituted carbazoles.
 7. The processaccording to claim 1 wherein said sulfuric acid solution containsgreater than about 80 wt. % sulfuric acid.
 8. The process according toclaim 2 wherein said sulfuric acid solution is obtained from analkylation process unit.
 9. The process according to claim 8 whereinsaid alkylation process comprises: a) combining an olefinic hydrocarbonfeedstream containing C₄ olefins with isobutane to form ahydrocarbonaceous mixture; and b) contacting the hydrocarbonaceousmixture with sulfuric acid under conditions effective for producing atleast an alkylate and a sulfuric acid solution having an acidconcentration of at least about 75 wt. %.
 10. The process according toclaim 7 wherein a diluent is added to said sulfuric acid solution toadjust the sulfuric acid concentration of said sulfuric acid solution.11. The process according to claim 1 wherein the sulfur concentration ofthe first and second hydrocarbon product streams is about 0.1 to about25 wt. % less than the respective first and second hydrocarbonfeedstreams.
 12. The process according to claim 1 wherein the yield lossattributed to the sulfuric acid solution treatment in the first andsecond contacting stages is about 0.5 to about 6 wt. %.
 13. The processaccording to claim 2 wherein the treat rate of the sulfuric acidsolution and the first used sulfuric acid solution is about 0.5 to about20 vol. %
 14. The process according to claim 13 wherein the firsthydrocarbon feedstream and the sulfuric acid solution and the secondhydrocarbon feedstream and the first used sulfuric acid solution areintimately contacted by a contacting method selected from non-dispersiveand dispersive contacting methods.
 15. The process according to claim 1wherein first hydrocarbon product stream and the first used sulfuricacid solution and second hydrocarbon product stream and the second usedsulfuric acid solution are separated by any means known to be effectiveat separating an acid from a hydrocarbon stream.
 16. The processaccording to claim 15 wherein the first hydrocarbon product and thefirst used sulfuric acid solution and the second hydrocarbon productstream and the second used sulfuric acid solution are separated by aseparation device selected from settling tanks or drums, coalescers,electrostatic precipitators, and other similar devices.
 17. The processaccording to claim 1 wherein said hydroprocessing process is selectedfrom hydrotreating, hydrocracking, ring opening, aromatics saturation,hydrodewaxing, and hydrofinishing.
 18. The process according to claim 1wherein said process further comprises contacting at least a portion ofsaid second hydrocarbon product stream with a hydroprocessing catalystin a hydroprocessing reaction stage.
 19. The process according to claim18 wherein said process further comprises separately contacting saidfirst and second hydrocarbon product streams with an effective amount ofan acid reducing material selected from caustic and water underconditions effective at reducing the total acid number of said first andsecond hydrocarbon product streams product prior to hydroprocessing. 20.The process according to claim 1 wherein at least one of the first andsecond hydrocarbon feedstreams is selected from non-hydrotreateddistillate or a blend of non-hydrotreated distillates.
 21. The processaccording to claim 20 wherein the sulfuric acid solution has an acidconcentration of greater than about 76 wt. %, a water concentration ofabout 2 wt. % to about 12 wt. %, and a dissolved oil concentration ofless than about 12 wt. %.
 22. The process according to claim 1 whereinat least one of the first and second hydrocarbon feedstreams is selectedfrom hydrotreated distillate, or a blend of hydrotreated distillates,each of which may or may not contain cracked stock.
 23. The processaccording to claim 22 wherein the sulfuric acid solution used to treatthe hydrotreated distillate, or a blend of hydrotreated distillates,each of which may or may not contain cracked stock, has an acidconcentration of greater than about 79 wt. %, a water concentration ofabout 2 wt. % to about 9 wt. %, and a dissolved oil concentration ofless than about 12 wt. %.
 24. The process according to claim 1 whereinat least one of the first and second hydrocarbon feedstreams is selectedfrom non-hydrotreated distillate or a blend of hydrotreated distillates,containing greater than 10% cracked stock, based on the distillate orblend.
 25. The process according to claim 24 wherein the sulfuric acidsolution used to treat the non-hydrotreated distillate or a blend ofhydrotreated distillates, containing greater than 10% cracked stock,based on the distillate or blend, has an acid concentration of greaterthan about 79 wt. %, a water concentration of about 2 wt. % to about 9wt. %, and a dissolved oil concentration of less than about 12 wt. %.26. The method according to claim 1 wherein at least one of the firstand second hydrocarbon feedstreams is selected from distillate boilingrange feedstreams containing greater than 40 wt. % cracked stock. 27.The process according to claim 26 wherein the sulfuric acid solutionused to treat the distillate boiling range feedstreams containinggreater than 40 wt. % cracked stock is used at a treat rate of about 3vol. % to about 6 vol. % based on the distillate boiling rangefeedstream.
 28. The method according to claim 1 wherein at least one ofthe first and second hydrocarbon feedstreams is selected from lube oilboiling range feedstreams.
 29. The method according to claim 28 whereinthe sulfuric acid solution used to treat the lube oil boiling rangefeedstreams contains about 85 wt. % to about 93 wt. % sulfuric acid, andabout 0.5 to about 5 wt. % water, with the remaining balance being acidsuspended hydrocarbons.
 30. The method according to claim 1 wherein atleast one of the first and second hydrocarbon feedstreams is selectedfrom raffinates.
 31. The method according to claim 30 wherein thesulfuric acid solution used to treat the raffinates contains about 92 toabout 88 wt. % sulfuric acid, about 1.5 to about 4 wt. % water, with theremaining balance being suspended hydrocarbons.